In regard to an imaging technology in which the distance in the depth direction can be obtained as two-dimensional array information, various methods are being studied such as a method of using a reference beam or a method of performing stereo distance measurement using a plurality of cameras. In recent years, as new distance measuring devices for civilian use, there is a high demand for products having a relatively moderate price.
In such imaging technology for obtaining distances, the triangulation method using parallaxes is known as one of the imaging methods in which a reference beam is not used with the aim of holding down the system cost. As the types of camera capable of implementing the triangulation method, a stereo camera and a multiple camera are known. However, in a stereo camera or a multiple camera, a plurality of cameras is used. Hence, there is a risk of an increase in the failure rate due to an increase in the size of the system or an increase in the number of components.
Meanwhile, regarding an imaging optical system, a structure has been proposed in which a microlens array is disposed on the upper side of pixels; a plurality of pixels is arranged in the lower part of each microlens; and an image from a main lens is further formed on the pixels using the microlens array. In this structure, a group of images having parallaxes can be obtained in the units of pixel blocks. The parallaxes enable performing a refocussing process based on distance estimation and distance information of a photographic subject. An optical configuration in which an image from a main lens is further formed using a microlens array is called a refocus optical system.
In a configuration in which the refocus optical system is used, the image formed due to each microlens is an image taken by shifting the position of the same photographic subject captured in the adjacent image. Hence, if the images formed due to the microlenses are superimposed while shifting positions thereof; it becomes possible to reconstruct a refocused image focused at an arbitrary specified distance in the image. Moreover, as a result, it becomes possible to obtain the distance to the position of the photographic subject specified in the images.
In a microlens array, in an area away from the optical axis of the main lens and having a greater image height, the microlens images undergo deformation due to vignetting. Thus, if an identical matching method is implemented in an area having a greater image height and in an area closer to the optical axis of the main lens and having a smaller image height, then there is a risk of a decline in the distance detection accuracy due to false detection of microlens edges or due to the matching error attributed to image distortion.